Shield structure for vacuum switches and the like



United States Patent 3,196,991 ElHEELl) STRUCTURE l lClR VACUUM SWITCEES AND THE LIKE Jo Emmett Jennings, San lose, Califi, assignor, by mesne assignments, to .lennings Radio Manufacturing Corporation, San Jose, Calilh, a corporation of Delaware Filed May 1, 1961, Ser. No. 106,894 9 Claims. (Cl. Mid-14.4)

This invention relates to vacuum switches or to other vacuum components incorporating a conductor from which metallic vapor or particles may be caused to emanate; and particularly to a means for shielding the interior of the switch or other envelope from vapor condensation or flying metallic particles resulting from arcing at the contacts or other separation of the conductor.

The main object of the invention is the provision of an improved shielding means which effectively prevents vapor condensation on the envelope and which means is easily assembled from relatively inexpensive parts.

Another object of the invention is the provision of a vapor condensing shield in a vacuum switch that is easily constructed from metal and at the same time readily insulated against short-circuiting.

Other objects will be apparent from the following specification and from the drawings.

FIG. 1 is a longitudinal section of a vacuum switch showing the shielding means and the conductor extending through the envelope, the conductor here being shown separated to provide spaced conductor ends within the envelope.

FIG. 2 is a cross section through a plane indicated by ection lines 22 of FIG. 1.

The invention contemplates a metallic shield which is readily degassed and acts as an effective repository for the vaporized metal, such as tungsten, which emanates from, for example, switch contacts.

Heretofore various types of shields have been employed for the purpose of preventing the deposit of vaporized tungsten on the vacuum switch envelope. Such varorized tungsten, if allowed to condense on the inner walls of the envelope, provides a conducting path between the inside terminals thus shorting the contact points and limitting the useful life of the switch.

Some previously used shielding devices have been supported by the contacts or connected to the terminals on which the contacts are mounted. Such a combination involves considerable diiiiculty in assembly and augments the likelihood of failure since a potential is actually applied to the shield. By the present invention the shielding means is not connected in any way with the source of potential and is spaced as far as possible from the contacts. This has further advantage of increasing the volume available for gas expansion during the interrupting cycle. Furthermore, by the present invention the shielding means is formed of separate spaced apart shielding members thus considerably reducing the potential difference that may exist between adiacent members.

Although the material from which the shielding means may be formed is not critical as far as the instant invention is concerned, it will be apparent that the means disclosed may incorporate inexpensive materials as well as simple mounting techniques.

In detail, and with reference to FIG. 1, the invention is illustrated as used with a vacuum switch having a fixed contact l and a mobile contact 2 but it will be apparent that the invention is just as applicable for use with other components such as the high-power fuse disclosed and claimed in applicants copending application Serial No. 240,212 filed November 23, 1962 as a continuation of copending application Serial No. 166,813 filed lune 13,

961 and now abandoned. A modified shield construction is disclosed and claimed in applicants copening application Serial No. 182,340 filed March 26, 1962. Although the particular base structure on which such conductor or contacts are supported may vary, the contacts 1, 2, of FIG. 1 are housed within a generally cylindrical glass shell 3 forming a sidewall which is closed at its ends by copper endwalls or caps 4, 5 connected to the glass by seal 6, thus forming a closed envelope. These caps 4, 5 constitute external terminals and also provide lugs 7, 8 respectively by which the switch may be conveniently mounted in suitable clips or brackets.

Brazed in lug 7 is a post lll which serves to support fixed contact 1. At the opposite end of the envelope a rod 12 is reciprocably mounted within an end plug 13 sealed in lug 8 and serves to support a post 14 which in turn carries mobile contact 2. A bellows 16 connects post 14 with plug 13 thus maintaining a tight seal while permitting movement of mobile contact 2 toward and away from fixed contact 1. As noted above, the particular means for mounting the contacts 1, 2 is not critical and the device shown in FIG. 1 is only one example of the various types of structures with which the invention may be employed. It is of course obvious from the foregoing that posts 11 and 14, bellows l6 and contacts 1 and 2 when in abutting relation constitute a conductor which extends between the endwalls of the envelope.

The shielding means comprises a plurality of similar tubular members surrounding the contacts ll, 2 and concentric with the axis which represents the line of action of the contacts. Although the number of tubular shielding members is not critical and will depend, to some extent, on the particular application, three such members are shown in FIG. 1 and are generally designated 20, 21, 22.

Each tubular member is formed to a smaller diameter at one end than at the other so that adjacent members may be partially nested within each other. This arrangement is preferably accomplished by forming each member with a small diameter cylindrical portion 24, a large diameter cylindrical portion and connecting said portions as shown by an annular integral flange 26. The flange defines the transition in each member from a relatively small diameter end to a relatively large diameter end.

The mounting means for shielding members Ell-2.2 comprises a plurality of circumferentialiy spaced dielectric rods 23 which extend alongside but spaced from the cylindrical glass shell 3 of the envelope and parallel to the common axis of contacts 1, 2. The ends of shell 3 may be conveniently formed with radially inwardly extending annular portions 29, 3t? thus providing opposed inwardly directed shoulders Ill, 32 against which the opposite ends of rods 23 may be abutted. In practice it is preferable to make the length of rods 23 slightly shorter than the spacing between shoulders 31, 32 for a reason which will subsequently become apparent.

Fixedly secured to the annular flange 26 of each of the shield members 2ll-22 are radially outwardly extending ears or tabs 34 in the nature of flanges which are apertured to receive rods 28 therethrough. interposed between the ears on member 26 and the next adjacent member 21 and surrounding rods 28 are tubular dielectric spacers 35, and interposed between the ears on member 21 and the next adjacent member 22 are tubular spacers 36. It will be apparent that spacers 35, 36 serve to space apart the members 29, 21, 22 whatever predetermined distance is desired. In a similar manner spacers 38 space member 20 from shoulder 32.

Between the ears 34 of shield member 20 and the shoullder 31 of the glass shell 3 tubular spacers 37 are interposed. However, said spacers 37 are not sufiiciently long to abut shoulder 31 and compression springs 40 are mounted on rods 23 with the opposite ends of said springs abutting shoulder 31 and the ends of spacers 3'7 respectively. In this manner the spacers 35-38 are placed under some compression thus insuring the desired spacing of shield members 2tl22 at all times. It will be noted in this connection that there is no tendency for rods 28 to shift since they are positively held in the apertures in cars 34.

The cars 34 are preferably formed of very light gauge material so that the free ends thereof may deflect somewhat to accommodate the shield members to the inside diameter of the glass shell 3, as indicated in FIG. 1. For this reason the cars 54 are made slightly'longer than would be required to just engage the glass shell 3.

It will be noted that the assembly of the above described structure is especially simple since the glass shell 3 is made in two parts which are joined along the line A-A after the assembly in each part of its related components. When said two parts are joined together prior to sealing, the springs 49 are placed under a slight compression which assures the correct spacing of the shield members ZAP-22 and at the same time provides a permanent positioning means for the entire assembly.

It will be noted that each small diameter portion 24 of the shielding members 21, 22 is spaced both axially and radially from the adjacent large diameter portions 25 of the members 25 21 thus insuring adequate electrical insulation between adjacent members. Since the rods 23 and the spacers cooperating therewith are of dieelectric material there is no possibility of short circuits. The use of a plurality of shielding members as above described provides, in effect, a voltage divider creating a potential gradient which reduces the voltages existing between adjacent parts thus enhancing the insulation between the switch terminals.

Additional shielding may be accomplished where required. For example, a dish-shaped shield 42 may be provided on post 11 to intercept the vapor and particles which might otherwise reach the fixed contact end of glass shell 3.

It will be seen that the above described shielding means is not only simple to assemble as an integral unit but per mits the shielding members to be placed relatively close to the glass shell 3 thus allowing a relatively large volume for gas expansion during the interru ting cycle of the contacts. Furthermore, because of the tortuous paths of travel imposed upon particles directed toward the glass shell an extremely effective shielding is obtained thus resulting in an unusually long life of the switch. 7

The above specific description of a preferred form of the invention should not be taken as restrictive thereof since variations in design will be apparent to those skilled in the art without departing from the scope of the following claims.

I claim:

I. In a vacuum component that includes a vacuumized envelope symmetrical about a longitudinal axis and having a pair of opposite endwalls and sidewalls of given interior diameter connecting said endwalls and at least one conductor extending through said envelope between said opposite endwalls and subject to separation intermediate its ends to interrupt conduction therethrough and to thereby provide spaced conductor ends within the envelope; spaced surfaces formed by said envelope wall adjacent opposite ends thereof constituting interiorly annular support surfaces substantially perpendicular to the longitudinal axis of the envelope, shielding means for shielding said sidewalls against impingement of metallic particles emanating from said conductor upon separation thereof including a cylindrical shielding member in coaxial relation to said conductor and disposed between said conductor and said sidewalls, and shield member support means including a plurality of circumferentially spaced elongated dielectric support rods extending between said annular support surfaces and alongside said sidewalls substantially parallel to said conductor to secure said shielding member to said envelope.

2. The combination according to claim It, in which said shielding member is provided with a plurality of radially extending apertured tabs equal in number to said rods and through which said rods extend.

3. The combination according to claim 2, in which said apertured tabs have a length such that the diameter across opposed tabs is greater than said given interior diameter of the sidewalls whereby the ends of said tabs are deflected and said shielding member is centered within the envelope.

4. The combination according to claim 1, in which a plurality of axially spaced shielding members are provided, and a tubular dielectric spacer is interposed about each rod between adjacent shielding members.

5. The combination according to claim 4, in which a tubular spacer is interposed between each said annular support surface and the adjacent shielding member at the occurrence of one of said rods to space said shielding means within the envelope with respect to the endwalls thereof, and a spring is resiliently interposed between at least one of said annular support surfaces and the shielding member support means.

6. The combination according to claim it, in which said shielding member is provided with a plurality of radially extending thin metallic tabs having a length such that the diameter across opposed tabs is greater than said given interior diameter of the sidewalls whereby the ends of said tabs are deflected and said shielding member is centered within the envelope.

7. In a vacuum component that includes a vacuumized envelope symmetrical about a longitudinal axis and having a pair of opposite endwalls and sidewalls of given in terior diameter connecting said endwalls and at least one conductor extending through said envelope between said opposite endwalls and subject to separation intermediate its ends to interrupt conduction therethrough and to thereby provide spaced conductor ends within the envelope; shielding means for shielding the interior of said sidewalls against impingement of metallic particles emanating from said conductor upon separation thereof including a plurality of axially spaced similar shielding members in surrounding relation to said conductor and spaced radially inwardly from the interior of said sidewalls a given amount to provide an annular space between said shield ing members and the interior of said sidewalls, each of said shielding members being generally cylindrical and formed of relatively thin sheet material, one end of each of said shielding members being of a smaller diameter than the opposite end and nesting within but radially spaced from the larger end of the next adjacent shielding member, shield support means disposed within said annular space between each said shielding member and the interior surface of said envelope to position and support said shielding members horizontally and vertically within the envelope and including a radially outwardly extending projection on each shielding member in the zone defining the transition in each member from a relatively small diameter end to a relatively large diameter end, di-

electric means disposed within said annular space and cooperating with said radially outwardly extending pro-- jection to position the shielding members with respect to said envelope and to electrically insulate said shielding members one from another and including an elongated dielectric support rod extending alongside said sidewalls and substantially parallel to the conductor, and a tubular dielectric spacer coaxially spaced along said support rod between each said radially outwardly extending projection and the next adjacent shielding member to space said members a predetermined distance apart axially of said envelope. Y

8. In an envelope for an electrical conductor from which a hot discharge of high velocity metallic particles may be caused to occur, an electrically discontinuous shield surrounding the conductor and comprising a plurality of overlapping cylindrical metallic units, and a plurality of circumferentially spaced dielectric spindles dis- 5 posed between the envelope wall and the outer periphery of the discontinuous shield to support the shield Within the envelope.

9. A structure in accordance with claim 8, in which each cylindrical unit includes a pair of cylindrical sections of different diameters and a radially extending flange on each cylindrical unit is engaged by a spindle.

References Cited by the Examiner UNITED STATES PATENTS 10 2 22 ,157 1 41 greenback 313 313 MAX LEVY, ROBERT SCHAEFER,

2,358,553 9/44 Beldi 313-239 6 5/50 Coolidge 313-240 5/56 Price 313240 6/59 Crouch 200-144 4/61 Schneider 200144 FOREIGN PATENTS 1/58 Italy.

BERNARD A. GlLI-IEANY, Primary Examiner.

Examiners. 

1. IN A VACUUM COMPONENT THAT INCLUDES A VACUUMIZED ENVELOPE SYMMETRICAL ABOUT A LONGITUDINAL AXIS AND HAVING A PAIR OF OPPOSITE ENDWALLS AND SIDEWALLS OF GIVEN INTERIOR DIAMETER CONNECTING SAID ENDWALLS AND AT LEAST ONE CONDUCTOR EXTENDING THROUGH SAID ENVELOPE BETWEEN SAID OPPOSITE ENDWALLS AND SUBJECT TO SEPARATION INTERMEDIATE ITS ENDS TO INTERRUPT CONDUCTION THERETHROUGH AND TO THEREBY PROVIDE SPACED CONDUCTOR ENDS WITHIN THE ENVELOPE; SPACED SURFACES FORMED BY SAID ENVELOPE WALL ADJACENT OPPOSITE ENDS THEREOF CONSTITUTING INTERIORLY ANNULAR SUPPORT SURFACES SUBSTANTIALLY PERPENDICULAR TO THE LONGITUDINAL AXIS OF THE ENVELOPE, SHIELDING MEANS FOR SHIELDING SAID SIDEWALLS AGAINST IMPINGEMENT OF METALLIC PARTICLES EMANATING FROM SAID CONDUCTOR UPON SEPARATION THEREOF INCLUDING A CYLINDRICAL SHIELDING MEMBER IN COAXIAL RELATION TO SAID CONDUCTOR AND DISPOSED BETWEEN SAID CONDUCTOR AND SAID SIDEWALLS, AND SHIELD MEMBER SUPPORT MEANS INCLUDING A PLURALITY OF CIRCUMFERENTIALLY SPACED ELONGATED 